1. Field of the Invention
The present invention relates in general to integrated circuit (IC) manufacturing and, more specifically, to methods in IC manufacturing processes for sorting IC devices using identification (ID) codes, such as fuse IDs, in the devices.
2. State of the Art
Integrated circuits (ICs) are small electronic circuits formed on the surface of a wafer of semiconductor material, such as silicon, in an IC manufacturing process referred to as “fabrication.” Once fabricated, ICs are electronically probed to evaluate a variety of their electronic characteristics, cut from the wafer on which they were formed into discrete IC dice or “chips,” and then assembled for customer use using various well-known IC packaging techniques, including lead frame packaging, Chip-On-Board (COB) packaging, and flip-chip packaging.
Before being shipped to customers, packaged ICs are generally tested to ensure they will function properly once shipped. Testing typically involves a variety of known test steps, such as pre-grade, burn-in, and final, which test ICs for defects and functionality and grade ICs for speed.
As shown in FIG. 1, a variety of data are collected as ICs proceed through an IC manufacturing process. For example, fabrication deviation data reflecting quality deviations, such as fabrication process errors, are collected during fabrication and summarized in one or more reports commonly referred to as “Quality Deviation Reports” (QDRs). Similarly, data are collected during probe which record the various electronic characteristics of the ICs tested during probe.
When any of the wafers in a wafer lot are deemed to be unreliable because they are low yielding wafers, as indicated by the collected probe data, or because they are misprocessed wafers, as indicated by the QDRs, all the ICs from the wafers in the wafer lot typically undergo special testing, such as enhanced reliability testing, that is more extensive and strict than standard testing. Since a wafer lot typically consists of fifty or more wafers, many ICs that undergo the special testing do not require it because they come from wafers that are not deemed unreliable. Performing special testing on ICs that do not need it is inefficient because such testing is typically more time-consuming and uses more resources than standard testing. Therefore, there is a need in the art for a method of identifying those ICs in a wafer lot that require special testing and sorting the ICs in the wafer lot into those that require special testing and those that do not.
As described in U.S. Pat. Nos. 5,301,143, 5,294,812, and 5,103,166, some methods have been devised to electronically identify individual ICs. Such methods take place “off” the manufacturing line, and involve the use of electrically retrievable identification (ID) codes, such as so-called “fuse IDs,” programmed into individual ICs to identify the ICs. The programming of a fuse ID typically involves selectively blowing an arrangement of fuses and anti-fuses in an IC so that when the fuses or anti-fuses are accessed, they output a selected ID code. Unfortunately, none of these methods addresses the problem of identifying and sorting ICs “on” a manufacturing line.